Ecohydraulic modelling to evaluate cascade dam construction impact and support fish habitat restoration

The cascade dam constructions in the Lancang River basin will alter the river's hydrological status and affect the habitat quality of spawning sites. In this study, an ecohydraulic model was proposed to evaluate the effects of the cascade dam construction and support the restoration of spawning sites. Four spawning sites and two fish species were selected as computational domains and target fish species, respectively. The Schizothorax prenanti and Schizothorax davidi represent dominant and protected fish species in all four spawning sites. Typical annual flow discharges were used to represent the flow pattern in the Lancang River. The hydrodynamic parameters and habitat indicators were simulated and used for ecological status evaluation. Three scenarios were proposed: pre-dam construction, after dam construction, and restoration strategies. The results indicated that the quality of the Schizothorax prenanti habitat is better than that of the Schizothorax davidi habitat in all scenarios, with Schizothorax prenanti mainly distributed in the middle of the river and Schizothorax davidi scattered along the riverside. The cascade dam construction will fragment spawning Sites 1 and 2 while it will improve the habitat status in Sites 3 and 4. In addition, with restoration strategies applied, the prediction indicates that the degree of fragmentation of the habitat at spawning Sites 1 and 2 can be significantly reduced. The post-restoration effects also proved the feasibility of these two recommended restoration strategies. The analysis indicated that the investigation of the Lancang River could yield valuable information about hydropower development and habitat protection.